The present invention relates to a method according to the superordinate concept of Claim 1.
Known methods of this kind are working with relatively simple B-scan imaging units, in which the position of the displayed sectional plane is determined only by way of the contact position of the ultrasound transducer and its orientation to the organ being examined. By even only small swings of the ultrasound transducer around the horizontal or vertical axis the position of the displayed sectional plane will be varied too. In addition, when scanning living organisms, by changes of the position of either the total body, or the organ being aimed at within the body or tissue layers, corrective actions will occur within the displayed sectional plane containing the xe2x80x9caiming pointxe2x80x9d within the organism. It is known to provide rigidly mounted guides on the ultrasound transducer for the biopsy needle or similar to be inserted mostly at a fixed distance from the ultrasound transducer toward the sectional plane determined by that ultrasound transducer. The xe2x80x9cidealxe2x80x9d direction within the sectional plane can be displayed in the B-mode image by way of a superposed auxiliary line. Also the biopsy needle or similar are being observed during the introduction. Even with a non-moving organism it is then difficult to determine whether an inexactly introduced biopsy needle leaves the displayed sectional plane in or against the aspect direction and to make appropriate corrections. In case of moving organisms, however, modifications in addition to corrections of the biopsy needle also of the contact direction, especially the contact inclination of the ultrasound transducer must be made, so that only very experienced medical doctors are able to really achieve the theoretically possible accuracy of this known method. From DE 24 25 724 A it is known to equip biopsy needles with a coating well reflecting ultrasound waves or with profiles to improve the visibility in the ultrasound image, but even this does not change anything in the above mentioned problems.
To increase the accuracy, according to AT 344 872 B two ultrasound transducers are used for a B-scan image which are connected at a distance and perpendicular to each other by a guiding device for a biopsy needle, so that the scan planes of the two ultrasound transducers intersect in a straight line within the object which is the introduction axis of the biopsy needle, determined by the biopsy needle guide. So if the aimed point in the object is on the straight line and is displayed in both images, the introduced biopsy needle will hit it with a high probability. Here also the above mentioned readjustment difficulties with moving organs or organs changing their position, the adjustment and readjustment of the ultrasound transducers becomes complicated and the examining doctor has practically no hand free to introduce the biopsy needle. Furthermore an instrument equipped this way can only be used for this single purpose and it is not always possible to fix the two ultrasound transducers to the object maintaining sufficient or good coupling quality, respectively.
It has to be mentioned here that such methods generally can be used for a great variety of purposes, i.e. for the withdrawal of fluid, tissue or other samples of organs, for punctures as well as for specific punctual treatments within organisms.
The purpose of the invention to be described herein is thus the creation of a novel method compared to those mentioned in the introduction, by which the accuracy of aiming and of introducing the biopsy needle or anything similar is improved at less critical coupling accuracy of the ultrasound transducer, ensuring also a high accuracy in case of moving organs or organs changing their position and which enables less experienced doctors to work safely with high accuracy.
The problem is solved in full by the characteristics of the method described in Claim 1. In principle, an ultrasound machine with an adequate ultrasound transducer which is subject of our own EP 0 962 785 A can be used to perform the method according to this invention. This machine is to be adapted to the conditions of the method according to the invention, especially as regarding the software, whereas in addition the mentioned sectional plane shall be displayed as a whole. The sectional plane however can be selected especially in case of machines without compulsory guiding device for the biopsy needle within the scanned total volume, whereby the adjustment is only necessary in so far as the partial volume surrounding the insertion path remains safely present within the scanned total volume. In case of ultrasound machines with compulsory guiding device, basically one will select that sectional plane for the display which lies in the target direction of the biopsy needle guide.
As in the 3D-display only the actual areas destined for the introduction of the biopsy needle and their close surroundings are made visible, this way of display is less confusing compared to a display in whole, but it offers the possibility to also visualize the curvatures of shapes within the organism being transverse to the imaged B-scan plane, which e.g. result from the surface shape or the shape of separating layers, so that the introduction point of the biopsy needle can be very accurately aimed at. Due to the 3D-display, the needle itself is well visible even when it slightly leaves the sectional image plane, thus facilitating corrections of the guidance of the needle in a way unknown before. In case of unmoving organs the limits of the selected partial volume can be set relatively close to the aiming axis. With moving organs or organs changing their position, the limits are set such that even in case of movements and without major position changes of the ultrasound transducer the aiming axis remains always within this selected partial volume. Hence in most cases a compulsory guiding device connected to the ultrasound transducer will even be unnecessary.
As already mentioned, the limiting areas of the partial volume can be selected according to different criteria. An extremely simple method is described in Sub-Claim 2.
The 3D-image display offers several further possibilities to increase the accuracy of introduction and for the precise determination of the direction of introduction. It is possible to rotate, tilt and turn round the partial image obtained by the 3D-method with methods already known, in order to examine it from all sides and to then select the direction of introduction and introduction point as wanted. Due to the customary way of image examination it also can show advantageous to align the 3D-image according to Sub-Claim 3.
The method according to the invention is not restricted to the sectional image and 3D-image technique, but can also be used with compatible methods as indicated in Claim 4. However, in case of Doppler-coded scanning a substantial decrease of the possible scan velocities will result in order to allow the Doppler evaluation. In Claim 5 a design is specified which proves excellent with a forced guidance of the instruments.